Corrosion inhibited lubricating compositions



United States Patent 3,296,127 CORROSION INHIBITED LUBRHCATING COMPOSITIONS Richard A. Butcosk, Westmont, and Henry Raich, Cherry Hill, N.J., assignors to Mobil Oil Corporation, a corporation of New York No Drawing. Filed Nov. 1, 1963, Ser. No. 320,924

9 Claims. (Cl. 252-25) This invention relates to lubricating compositions suitable for use over a Wide range of operating conditions. In one of its aspects, the invention relates to lubricating compositions containing certain materials which exhibit corrosion or rust-inhibiting characteristics when incorporated in these compositions. Still more particularly, in this aspect, the invention relates to lubricating grease compositions exhibiting the aforementioned corrosion-inhibiting characteristics, and to a method for their preparation.

In the preparation of lubricating compositions, as for example, greases and other lubricants of varying viscosities, it has been the practice to incorporate in these compositions various corrosion or rust-inhibiting materials to avoid the deleterious effect upon metal surfaces being lubricated, when such surfaces are continuously or intermittently subjected to humid or wet environmental conditions. Among the corrosion-inhibiting materials that have been suggested for this purpose are the alkali metal nitrites, which are well known for their corrosioninhibiting properties. Of particular importance, in this respect, is sodium nitrite. In general, it has been found that in order to achieve a fairly adequate degree of corrosion-inhibiting effect in the aforementioned lubricating compositions, the alkali metal nitrite should be employed in the lubricant in an amount equal to at least about 2 percent, by weight, of the total lubricating composition.

In this respect, however, it has also been found that the presence of even such low concentrations of alkali metal nitrite results in the abrasion and deterioration of the metal surfaces being lubricated by the grease or other lubricating composition. On the other hand, the use of lower concentrations of the alkali metal nitrite in the lubricant, does not result in imparting sufficient corrosionresistant properties to the latter. Thus, prior to the present invention no effective and relatively simple method has been proposed for the incorporation of alkali metal nitrites in lubricating compositions in relatively small concentrations and which, nevertheless, still impart adequate corrosion-resistant properties to the lubricant.

It is, therefore, an object of the present invention to provide improved corrosion-inhibiting materials for lubricating compositions.

Another object of the invention is to provide improved corrosion-inhibiting materials, comprising alkali metal nitrites, for lubricating compositions.

Still another object of the invention is to provide lubricating compositions having improved corrosion-inhibiting properties, and wherein metallic surfaces being lubricated by these compositions are not significantly abraded or otherwise damaged.

A still further object of the invention is to provide a method for preparing the aforementioned lubricating compositions.

Other objects and advantages inherent in the invention will become apparent to those skilled in the art from the following description.

In prior application Serial No. 319,497, filed October 28, 1963, in the name of Richard A. Butcosk, a co-inventor of the present application, there is disclosed that lubricating compositions having effective and useful corrosion and rust-inhibiting properties may be prepared employing relatively small amounts of alkali metal nitrites, as the inhibitors, when used in conjunction with a N- carboxymethyl-alkenyl-succinamic acid. The synergistic effect of such additive combination makes it possible to employ such small quantities of the alkali metal nitrite and the succinamic acid, that metallic surfaces being lubricated are not abraded or otherwise damaged by the nitrite component in the lubricating composition. In that application, it was further pointed out that it was also found that this ability of the lubricating composition to exhibit effective corrosion-inhibiting properties, although employing relatively small amounts of the nitrite component, could not otherwise be achieved except for the presence, and the synergistic effect, of the aforementioned succinamic acid component.

In preparing the improved lubricants containing the inhibitor compositions of the aforementioned application Serial No. 319,497, it was indicated that if the alkali metal nitrite and the N-carboxymethyl-alkenyl-succinamic acid were to be added to the lubricant under substantially anhydrous conditions, i.e. either as solids or in the presence of a non-aqueous vehicle for one or both of the components, these components could be incorporated into the lubricant either separately, and in any sequence; or they could first be admixed, and, thereafter, the thus pre-formed inhibitor composition could be incorporated therein. If, on the other hand, the inhibitor components were to be added under aqueous conditions, it would be essential that the aqueous nitrite components would first be incorporated into the lubricant while the latter is maintained at an elevated temperature sufiicient to drive off water present, and the succinamic acid'would thereafter be added. This sequence is necessitated because of the fact that if the succinamic acid were first incorporated into the lubricant, the succinamic acid being reactively acid would cause the nitrite to decompose and liberate nitrous oxide under the aqueous conditions present, thereby rendering the nitrite component ineffective as the corrosion inhibitor and also bring about corrosion of the metal surfaces being lubricated.

In accordance with the present invention, it has now been found that aqueous solutions of the alkali metal nitrite may be employed for the purpose indicated, without the necessity of being first incorporated into the lubricant, while the latter is maintained at an elevated temperature in order to drive off Water present, and with the succinamic acid being thereafter added. In this respect, as more fully hereinafter described the present invention provides a novel corrosion-inhibitor composition, for lubricants, comprising, as the inhibitor components, an alkali etal nitrite, an N-carboxymethyl-alkenyl-succinamic acid and an alkali metal phosphate. In general, the inhibitor is prepared by combining an aqueous solution of the alkali metal phosphate with the N-carboxymethylalkenyl-succinamic acid, in order to neutralize the normally acid state of the succinamic acid by raising the pH value of the latter to 7 or higher, and thereafter adding to the thus-obtained non-acidic succinamic acid reaction product an aqueous solution of the alkali metal nitrite, to form the final corrosion-inhibitor composition which is to be incorporated into the lubricant. The thus-prepared inhibitor may, also, first be heated to drive off part, or all, of the water present before being incorporated into the lubricant, if so desired. Alternatively, the aforementioned non-acidic succinamic acid reaction product may be first incorporated into the lubricant composition, followed by the incorporation of the aqueous alkali metal nitrite solution. By proceeding in this manner, the necessity for first incorporating the aqueous metal nitrite component into the lubricant and driving off Water before the succinamic acid is added, as disclosed in the aforementioned application Serial No. 319,497, is obviated.

Insofar as the components comprising the corrosion inhibitor are concerned, the alkali metal nitrites which may be employed include sodium nitrite, potassium nitrite and lithium nitrite. Of these, sodium nitrite is preferred. The alkali metal nitrite is generally employed in the inhibitor composition in an amount from about 15 to about 70 percent, by weight, and preferably in an amount from about 30 to about 50 percent, by weight of the total in hibitor composition.

As indicated above, an N-carboxymethyl-alkenyl-succinamic acid is employed in conjunction with the alkali metal nitrite and the alkali metal phosphate in the inhibitor composition for its synergistic effect. These succinamic acids can be prepared by several methods known to those skilled in the art. In general, they can be prepared by reacting an alkenyl succinic acid anhydride or an alkenyl succinic acid with glycine (aminoacetic acid), in equi molar amounts and with the elimination of water of condensation, when the acid is employed. Accordingly, the reaction will be carried out at temperatures of between about 90 C. and about 120 C. The time of reaction will be dependent, of course, upon the reaction temperature employed. Reaction will take place readily when the acid anhydride is employed. When the acid is employed, reaction will continue until the required amount of water of condensation has evolved. Generally, the time will vary between about 6 to about hours, and shorter reaction times are required if water is removed by azeotropic distillation. Suitable liquids which form azeotropes with Water are non-polar solvents, such as benzene, toluene, and xylene.

The alkenyl succinic acid anhydride reactant can, generally, have from about 8 to about 35 carbon atoms in the alkenyl radical, particularly when employed in grease compositions, and preferably from about 10 to about 14 carbon atoms. Non-limiting examples of the alkenyl succinic acid anhydride reactants are oetenyl succinic acid anhydride, diisobutenyl succinic acid anhydride, 2-methylheptenyl succinic acid anhydride, 4-ethylhexenyl succinic acid anhydride, nonenyl succinic acid anhydride, decenyl succinic acid anhydride, dodecenyl succinic acid anhydride, triisobutenyl succinic acid anhydride, tetrapropenyl succinic acid anhydride, tetradecenyl succinic acid anhydride, hexadenenyl succinic acid anhydride, ll-tricosenyl succinic anhydride, and 17-pentatriacontenyl succinic anhydride. As mentioned hereinbefore, the alkenyl succinic acids corresponding to these alkenyl succinic acid anhydrides can also be used to prepare the succinamic acids employed in the inhibitor composition. The preparation of the aforementioned N-carboxymethyl-alkenyl-succinamic acids is more fully discussed in US. Patent No. 3,039,861, issued June 19, 1962. The N-carboxymethylalkenyl-succinamic acid is generally employed in the inhibitor composition in an amount from about 5 to about 70 percent, by weight, and preferably in an amount from about 25 to about 40 percent, by weight, of the total inhibitor composition.

The alkali metal phosphates which may be employed include sodium phosphate, potassium phosphate and lithi- 11m phosphate, in any of their monobasic, dibasic or tribasic forms. Of these, sodium phosphate is preferred. 'The alkali metal phosphate is generally employed in the inhibitor composition in amount from about 3 to about "70 percent, by weight, and, preferably, in an amount from about 25 to about 50 percent, by weight, of the total inhibitor composition.

The quantity of the corrosion inhibitor employed will depend upon the characteristics of the lubricating composition being treated and the nature of the environmental conditions encountered by the lubricant in performing its function. In general, the more viscous types of lubricating compositions, for example, those which are normally classified as greases, may contain the aforementioned inhibitors which comprise from about 0.2 to about 5.0 percent, by weight, and, preferably, in an amount from about 0.2 to about 0.5 percent, by weight, of the total lubricant composition. The amount of alkali metal nitrite present may comprise from about 0.1 to about 2.0 percent, by weight, and, preferably, from about 0.25 to about 1.0 percent, by weight, of the total lubricant composition. The amount of N-carboxymethyl-alkenyl-succinamic acid present may comprise from about 0.1 to about 1.5 percent, by weight, and, preferably, from about 0.2 to about 0.5 percent, by weight, of the total lubricant composition. The alkali metal phosphate present may comprise from about 0.05 to about 1.5 percent, and, preferably, from about 0.1 to about 0.75 percent, by weight, of the total lubricant composition.

The following examples will serve to illustrate the preparation of typical improved corrosion-inhibitor compositions of the present invention, and their incorporation and performance in various lubricant compositions.

A base grease comprising an acetate complex in an ester fiuid, having the characteristics shown below, was treated, first with aqueous sodium nitrite (Example 2); then with the combination of aqueous sodium nitrite and N-c-arboxymethyl-tetrapropenyl-succinamic acid (Example 3); and, finally, with the combination of aqueous sodium nitrite, N-carboxymethyl-tetrapropenyl-succinamic acid and aqueous sodium phosphate (tri-basic). In the examples, aqueous solutions of sodium nitrite, having a concentration of approximately 40 percent, by weight, and an aqueous solution of sodium phosphate having a concentration of approximately 20 percent, by weight, were employed. In Example 3 the aqueous sodium nitrite solution was first incorporated in the grease, water was then driven off by heating, and the succinamic acid was thereafter added. In Example 4 the inhibitor composition was prepared by first reacting the succinamic acid with the aqueous sodium phosphate solution to obtain a slightly basic reaction product, thereafter, the aqueous sodium nitrite solution was added and water present was evaporated, prior to incorporating the three-component inhibitor into the grease. In each of the Examples 1 through 4 the respective grease formulations were next subjected to the Bearing Rust Protection Test ASTM D-1743, with the respective ratings, in each instance, being recorded as shown.

Base grease A: Parts by wt. Calcium acetate. /2H O 8.9 Calcium caprylate.5 %H O 6.1 Sodium hydroxy stearate 3.3 Antioxidant 1 2.0 Synthetic ester 2 Balance 1 Dioctyl diphenylamine plus 2,6-ditertiarybutyl p-cresol.

2 Tricaprylate of trimethylol propane.

N-earboxy- Bearing methyltetra- Na3P04.12H10 Protection Example NaNOz propenyl- (parts by wt.) Test, ASTM (parts by succinamic D-1743 wt.) acid (parts Rating 1 by wt.)

1 (Blank) #3,#3 2 25 #3,

1 #1 rating-n0 spots on outer cup raceway or on rollers (excellent).

#2 rating-A to 3 very small spots (fair).

#3 rating-more than 3 spots (poor).

From the above data of Examples 1 through 4, it will be apparent that the incorporation of the alkali metal phosphate in combination with the nitrite and succinamic acid in lubricant compositions, in the manner described, results in permitting the lubricant to satisfactorily pass a rigor-ous standard rust test, as shown in Example 4, and as contrasted with the inferior results shown in Examples 1, 2 and 3.

Following the procedure described above with respect to the use of base grease A, in Examples 1 through 4, base grease B, comprising an inorganic gelling agent (via, an amine-exchanged bentonite clay), in a lubricating oil,

r as was substituted for base grease A. Base grease B had the following characteristics, and the data obtained with this grease are shown in Examples 5 and 6.

From the above data of Examples 5 and 6, it will be seen that the incorporation of the novel inhibit-or composition, comprising the alkali metal nitrite, succinamic acid and the alkali metal phosphate, materially enhances the corrosion inhibiting properties of the lubricant composition, as shown in Example 6, when compared with the absence of the inhibitor composition, as shown in Example 5.

Following the procedure described above with respect to the use of base grease A, in Examples 1 through 4, and base grease B in Examples 5 and 6, base grease C, comprising a lithium soap in a mineral oil, was substituted for base greases A and B. Base grease C had the following characteristics, and the data obtained with this grease are shown in Examples 7 through 11.

From the above data of Examples 7 through 11, it will be seen that the incorporation of the novel inhibitor composition comprising the alkali metal nitrite, succinamic acid and the alkali metal phosphate, materially enhances the corrosion inhibiting properties of the lubricant composition, as shown in Examples 8 through 11, when compared with the absence of the inhibitor composition as shown in Example 7. It will be understood, of course, that other alkali metal nitrites may be substituted for the sodium nitrite, and that other N-carboxymethyl-alkenylsuccinamic acids may be substituted for the N-carboxymethyl-tetrapropenyl-succinamic acid, and that other alkali metal phosphates may be substituted for the sodium phosphate, as shown in the above examples, and that corrosion inhibitors containing these components may be incorporated in a wide variety of lubricant compositions.

While preferred embodiments of the compositions of 6 the present invention and the process for their preparation have been described for the purpose of illustration, it should be understood that various modifications and adaptations thereof, which will be obvious to those skilled in the art, may be made without departing from the spirit of the invention.

We claim:

1. A composition consisting essentially of (a) a product produced by neutralizing an N-carboxyrnethyl-alkenylsuccinamic acid, said al'kenyl group containing from about 8 to about 35 carbon atoms, with an alkali metal phosphate, said product having a pH of at least 7, and (b) an alkali metal nitrite.

2. The composition as defined in claim 1 wherein the alkenyl group contains from about 10 to about 14 carbon atoms.

3. The composition as defined in claim 1 wherein said N-carboXymethyl-alkenyl-succinamic acid is N-carboxymethyl-tetrapropenyl-succinamic acid, said alkali metal phosphate is sodium phosphate and said alkali metal nitrite is sodium nitrite.

4. The composition as defined in claim 1 wherein said N-carboxymethyl-alkenyl-succinamic acid is present in an amount from about 5 to about percent, by weight; said alkali metal phosphate is present in an amount from about 3 to about 70 percent, by weight; and said alkali metal nitrite is present in an amount from about 5 to about 70 percent, by weight.

5. The composition as defined in claim 1 wherein said N-carboxymethyl-alkenyl-succinamic acid is present in an amount from about 25 to about 40 percent, by weight; said alkali metal phosphate is present in an amount from about 25 to about 50 percent, by weight; and said alkali metal nitrite is present in an amount from about 30 to about 50 percent, by weight.

6. A lubricant composition containing, as a corrosion inhibitor, a composition as defined in claim 1.

7. A grease composition containing, as a corrosion inhibitor, a composition as defined in claim 1.

8. A lubricant composition containing from about 0.2 to about 5.0 percent, by weight, of the lubricant, as a corrosion inhibitor, a composition as defined in claim 1.

9. A grease composition containing from about 0.2 to about 5.0 percent, by weight, of the grease, as a corrosion inhibitor, a composition as defined in claim 1.

References Cited by the Examiner UNITED STATES PATENTS 2,748,081 5/1956 Peterson et al 252-25 X 2,780,597 2/1957 Williams et al 252-25 X 3,000,819 9/1961 Norton et al 252-25 3,039,861 6/1962 Andress et al. 4471 3,065,176 11/1962 Blake et a1. 252-25 X 3,089,848 5/1963 Morway 252-25 X 3,178,367 4/1965 Dubin et al. 252-25X FOREIGN PATENTS 892,266 3/1962 Great Britain.

DANIEL E. WYMAN, Primary Examiner. P. P. GARVIN, Assisiant Examiner. 

1. A COMPOSITON CONSISTING ESSENTIALLY OF (A) A PRODUCT PRODUCED BY NEUTRALIZING AN N-CARBOXYMETHYL-ALKENYLSUCCINAMIC ACID, SAID ALKENYL GROUP CONTAINING FROM ABOUT 8 TO ABOUT 35 CARBON ATOMS, WITH AN ALKALI METAL PHOSPHATE, SAID PRODUCT HAVE A PH OF AT LEAST 7, AND (B) AN ALKALI METAL NITRITE.
 6. A LUBRICANT COMPOSITION CONTAINING, AS A CORROSION INHIBITOR, A COMPOSITION AS DEFINED IN CLAIM
 1. 